Pearling, de-branning, flaking, milling (grinding), sieving and air-classification are standard dry technologies for the processing of grains such as oats and barley into their component concentrates such as fiber, starch and protein. Among these dry processing technologies, the processes of milling and sieving (using sieves attached to a sieve shaker and/or vibrators) are the most commonly used and economical methods. Sieving technology typically employs sieves with openings as small as 100 μm to separate and classify milled particulates based on their particle size. When fine sieves with openings of 100 μm or less are used, clogging tends to occur and this requires slowing down the feeding rate, leading to less throughput. This causes losses in separation efficiency, and with some plant materials, it becomes impossible to continue the sieving operation. Other existing methods based on pin-milling and air-classification (PMAC) technology show efficient separation of finer particulates but suffer from low extraction rates and poor yields of targeted components. Many studies on the air-classification of grain flours from cereals, pulses, and defatted oilseed meals have been conducted. In addition, PMAC technology is extraordinarily capital intensive, with the upfront costs of equipment often exceeding $1 million to begin commercial scale production.
A review of the prior art reveals that various air classification methodologies and equipment have been used in the past that utilize a variety of different techniques to effect separation of grain components. Such methodologies include various air flow techniques and equipment designs that subject the grain to different air flows that enable component separation.
For example, U.S. Pat. No. 5,348,161 to Mueller describes an apparatus for cleaning semolina which circulates air upwards through the bottom of a sieve to separate grain fractions and selectively collects the fractions in a closed system which prevents entry and exit of dust.
U.S. Pat. No. 8,061,523 to Uebayashi, et al. describes a purifier apparatus with a vibrating sieve box and stacked sieves. The purifier operates using regulated suction updraft to spread the particles width-wise along the sieve box with respect to the direction of stacking of the sieves.
U.S. Pat. No. 4,806,235 to Mueller describes an apparatus for cleaning grain products which has vibrating superimposed screen layers. Upward vacuum suction is provided with respect to the downward direction of travel of particles though the shaking screen. Suction is regulated by flaps.
U.S. Pat. No. 4,680,107 to Manola describes a separator device with a conical tray for spreading product while it moves from an inlet under suction. The product then meets an ascending flow of air sucked from the outside by the same suction mechanism. Heavier product drops to the bottom of the container for evacuation while lighter product remains suspended and follows the flow of air exiting the device via the suction conduit.
U.S. Pat. No. 5,019,242 to Donelson describes an apparatus for cleaning particulate material. A supply auger is used to introduce material to a discharge duct for deposit onto a vibrating screen. Fine material or light-weight debris passes through the screen and is then pulled outward and upward by vacuum pull through a conduit to a collection hopper. The heavier material (whole kernel material) is deposited on a discharge auger for collection.
U.S. Pat. No. 7,424,956 to Kohno describes a separation method and device for separating lightweight grains from raw grains. In a primary separation step, the grain mixture is whirled upward with primary air along the inner wall of the cylindrical section for allowing raw grains and part of the lightweight grains to stay in a certain flow area by frictional resistance with respect to the wall surface generated by whirl, and to drop into the conical section on the downside by their own weight. Certain embodiments also use secondary and/or tertiary airflows induced by blowers.
U.S. Pat. No. 5,645,171 to Felden describes an apparatus for sorting seeds or other objects. The seeds are introduced via a delivery module into a column and lifted upwards by vacuum suction until they exit the top of the column and pass over three separate collection chambers where they are collected according to density with the lightest components proceeding towards the vacuum source.
U.S. Pat. No. 7,976,888 to Hellweg et al. describes a dry milling process for preparing oat products enriched in beta-glucan. The process involves a series of milling, bolting (fractionating) and blending steps.
U.S. Pat. No. 7,910,143 to Kvist et al. describes a process for extraction of soluble dietary fiber from oat and barley grains for producing a fraction rich in beta-glucans. The process involves milling, enzymatic treatment with starch degrading enzymes and centrifuging.
US 2011/0253601 to Kaiser et al. describes an air jet sieve device for a batch processing method proposed mainly for the determination of particle size distribution at lab scale with a sieve disposed on a sieve deck and a chamber with a rotating slotted nozzle below the sieve deck, through which air is blown upwards to purge the sieve apertures and agitate material lying on the sieve. The chamber above the sieve deck is sealed during sieving. This device is equipped with a sensor for detecting particles in the air outlet flow from the chamber underneath the sieve.
U.S. Pat. No. 4,261,817 to Edwards et al. describes a sieving apparatus (batch processing) with a suction chamber, upon which sits a sieve support structure (levitation head) defined by a central bore and two additional rings of bores. A sieve cloth sits on the top surface of the levitation head. A sieve case structure is supported by the top surface of the levitation head. The levitation head also has horizontal air passages that permit entry of air into the sieve case. This air flow serves to agitate the material being sieved and prevents blockage of the sieve. Air also flows into the sieve case through two apertures in the top cover of the sieve case.
U.S. Pat. No. 4,268,382 to Hanke et al. describes an apparatus for separating solids from a suspension. The suspension is introduced into the device through an inlet where it accumulates in a stilling chamber until it passes over an overflow edge and runs down along a sieve provided with sieving bars and gaps. The fluid drains through the gaps and the solids are transferred over the gaps and discharged through a bottom chute.
EP 0978328B2 to Kaiser et al. describes a device which is generally similar to that described in US 2011/0253601, with additional electronic control mechanisms associated with the device.
In view of the foregoing, there continues to be a need for an improved high-throughput commercial scale sieving apparatus, system and method, which is continuous and non-clogging for dry fractionation of grain to produce separate fractions enhanced in fiber, starch and/or protein with high extraction efficiency of the aforementioned targeted components at low capital and processing costs.